The present invention relates generally to dosimetry and more particularly to a temporal dosimeter that records the exposure to dosages of ionizing radiation as a function of time over an extended time period.
Individuals working near ionizing radiation must be able to determine their radiation dosage since they risk developing radiation-induced injuries and sickness if exposed to large dosages. Workers who can efficiently detect an already excessive dosage could leave the area and avoid additional exposure, and seek medical attention if necessary. Dosimeters are typically provided to these workers. Dosimeters typically include a sensor enclosed within a protective housing. A measurable chemical and/or physical change is produced in the sensor when it is exposed to a particular radiation dosage. The protective dosimeter housing is generally composed of materials chosen to selectively absorb at least one type of radiation while transmitting other types. An opaque housing, for example, can absorb electromagnetic radiation in the visible region. A thin plastic housing can absorb alpha radiation but transmit beta radiation. A cardboard, aluminum, or thick plastic housing can absorb both alpha and beta radiation, while a lead housing can absorb even more penetrating radiation such as gamma and x-ray radiation.
Some types of dosimeters provide the total dosage. Others provide the dosage of a particular type of radiation. Still others provide both the total dosage and/or a radiation profile of the relative contribution of the various types of radiation to the cumulative, i.e. total, dosage. Some dosimeters may include a meter that provides a numerical value related to a particular dosage. Other dosimeters may include a chemical mixture that interacts with radiation to produce detectable color and/or opacity changes that indicate exposure to a particular dosage.
A wide variety of sensors have been used with dosimeters. Silver-containing sensors are among the most sensitive since silver has a high absorption cross section for many different types of radiation (see xe2x80x9cRadiation Dosimetryxe2x80x9d, vol. II, chapter 15; and Radiation Dosimetry: vol. III, chapter 28, hereby incorporated by reference). Film badges are among the most widely used dosimeters employing silver-containing sensors (see xe2x80x9cThe Use of Film Badges for Personnel Monitoringxe2x80x9d by M. Ehrlich, International Atomic Energy Agency, Vienna, 1962, hereby incorporated by reference). A film badge sensor is generally an emulsion of microscopic silver halide crystals dispersed in gelatin. The emulsion is coated onto a support to form a film. Images are produced on the film after it is exposed to radiation. The images can be in the form of particle tracks and an analysis of the tracks can provide the identity and the energy of the particles that produced the tracks.
A film badge dosimeter may be configured such that one portion of the film records the dosage of one type of radiation while other portions record other types of radiation. Film badges, therefore, provide a record of the cumulative dosage and a radiation profile for the cumulative dosage. The images recorded by a film badge sensor are related to the cumulative exposure for a single time period. One cannot, however, determine from a single film badge, how the cumulative dosage was accumulated over time. A separate film badge would be required for each time interval, and a separate analysis would be required for each badge.
A single, highly sensitive dosimeter that provides a record of how a dosage is accumulated over an extended time period remains desirable. Therefore, an object of the present invention is to provide a highly sensitive dosimeter that shows how a dosage is accumulated over an extended period of time.
Another object of the present invention is a dosimeter that provides the cumulative dosage of ionizing radiation for an extended time period, dosages for time intervals during that time period, and the radiation profile for the dosage obtained during each interval.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the objects and purposes of the present invention, as embodied and broadly described herein, the present invention includes a temporal dosimeter. The dosimeter includes a sensor for recording dosages of ionizing radiation. The dosimeter also includes means for shielding the sensor from visible light. The shielding means shields a major portion of the sensor from ionizing radiation while unveiling a minor portion of the sensor to ionizing radiation. The shielding means includes multiple apertures, each aperture being selectively permeable to a different type, or types, of ionizing radiation. The dosimeter also includes means for changing the relative position of the sensor and the radiation shield to unveil previously shielded minor portions of the sensor while shielding the remaining major portion of the sensor.
The invention also includes a temporal dosimeter having a sensor for recording dosages of ionizing radiation. The sensor has a first side and a second side. The dosimeter also includes a rotatable, first radiation shield having a shield portion for shielding a major portion of the first side of the sensor from ionizing radiation, and an aperture portion for unveiling a minor portion of the sensor to ionizing radiation. The dosimeter also includes a rotatable, second radiation shield having a plurality of apertures configured such that the rotatable first shield and the rotatable second shield together produce a compound aperture for unveiling different portions of the sensor. The dosimeter also includes a third radiation shield for shielding the second side of the sensor from ionizing radiation. The dosimeter also includes a drive mechanism having a rotatable shaft. The shaft is coupled to the rotatable first radiation shield and to the rotatable second radiation shield to rotate these shields. The dosimeter also includes a power source for driving the drive mechanism. The dosimeter also includes a housing for enclosing the sensor and the shield. The housing is opaque to visible light but transparent to at least one type of ionizing radiation.
The invention also includes a temporal dosimeter having a sensor for recording dosages of ionizing radiation. The dosimeter includes a radiation shield having a shield portion and an aperture portion, the shield portion being opaque to visible light and to ionizing radiation, the aperture portion being opaque to visible light but transparent to at least one form of ionizing radiation. The dosimeter also includes a drive mechanism that includes a linear actuator. The linear actuator is coupled to the sensor and moves the sensor past the aperture portion of the radiation shield so that the sensor turns as it moves past the aperture portion. This way, the sensor records a timeline record of exposure to ionizing radiation along a helical path on the sensor. The dosimeter also includes a power source for driving said linear actuator.
Unveiling a minor portion of a sensor to ionizing radiation using multiple apertures, each aperture being selectively permeable to a different type or types of ionizing radiation; then shielding the minor portion from ionizing radiation after a time interval, thereby recording a separate radiation dosage on the first minor portion for each aperture; and repeating the steps of unveiling and shielding for at least one other minor portion of the sensor to produce a timeline record of exposure to ionizing radiation.